feat: add dynamic filtering and pagination for Department search API

src/main/java/com/ainigma100/departmentapi/repository/DepartmentRepository.java

@@ -5,19 +5,20 @@
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.JpaSpecificationExecutor; // << add this
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.query.Param;
 
-public interface DepartmentRepository extends JpaRepository<Department, Long> {
+public interface DepartmentRepository extends JpaRepository<Department, Long>, JpaSpecificationExecutor<Department> {
 
     Department findByDepartmentCode(String departmentCode);
 
 
     @Query(value = """
             select dep from Department dep
-            where ( :#{#criteria.departmentCode} IS NULL OR LOWER(dep.departmentCode) LIKE LOWER( CONCAT(:#{#criteria.departmentCode}, '%') ) )
-            and ( :#{#criteria.departmentName} IS NULL OR LOWER(dep.departmentName) LIKE LOWER( CONCAT(:#{#criteria.departmentName}, '%') ) )
-            and ( :#{#criteria.departmentDescription} IS NULL OR LOWER(dep.departmentDescription) LIKE LOWER( CONCAT('%', :#{#criteria.departmentDescription}, '%') ) )
+            where ( :#{#criteria.departmentCode} IS NULL OR LOWER(dep.departmentCode) LIKE LOWER(CONCAT(:#{#criteria.departmentCode}, '%')) )
+            and ( :#{#criteria.departmentName} IS NULL OR LOWER(dep.departmentName) LIKE LOWER(CONCAT(:#{#criteria.departmentName}, '%')) )
+            and ( :#{#criteria.departmentDescription} IS NULL OR LOWER(dep.departmentDescription) LIKE LOWER(CONCAT('%', :#{#criteria.departmentDescription}, '%')) )
             """)
     Page<Department> getAllDepartmentsUsingPagination(
             @Param("criteria") DepartmentSearchCriteriaDTO departmentSearchCriteriaDTO,

src/main/java/com/ainigma100/departmentapi/service/impl/DepartmentServiceImpl.java

@@ -44,21 +44,27 @@ public DepartmentDTO createDepartment(DepartmentDTO departmentDTO) {
     }
 
     @Override
-    public Page<DepartmentDTO> getAllDepartmentsUsingPagination(
-            DepartmentSearchCriteriaDTO departmentSearchCriteriaDTO) {
+    public Page<DepartmentDTO> getAllDepartmentsUsingPagination(DepartmentSearchCriteriaDTO departmentSearchCriteriaDTO) {
 
-
-        Integer page = departmentSearchCriteriaDTO.getPage();
-        Integer size = departmentSearchCriteriaDTO.getSize();
+        // defensive defaults
+        Integer page = departmentSearchCriteriaDTO.getPage() == null ? 0 : departmentSearchCriteriaDTO.getPage();
+        Integer size = departmentSearchCriteriaDTO.getSize() == null ? 10 : departmentSearchCriteriaDTO.getSize();
         List<SortItem> sortList = departmentSearchCriteriaDTO.getSortList();
 
-        // this pageable will be used for the pagination.
+        // create Pageable using existing utility (keeps your sorting logic)
         Pageable pageable = Utils.createPageableBasedOnPageAndSizeAndSorting(sortList, page, size);
 
-        Page<Department> recordsFromDb = departmentRepository.getAllDepartmentsUsingPagination(departmentSearchCriteriaDTO, pageable);
+        // Build Specification from criteria
+        var spec = com.ainigma100.departmentapi.specification.DepartmentSpecification.fromCriteria(departmentSearchCriteriaDTO);
+
+        // Query repository using Specification + Pageable
+        Page<com.ainigma100.departmentapi.entity.Department> recordsFromDb =
+                departmentRepository.findAll(spec, pageable);
 
+        // Map entity list to DTO list
         List<DepartmentDTO> result = departmentMapper.departmentToDepartmentDto(recordsFromDb.getContent());
 
+        // Return a page preserving the paging metadata
         return new PageImpl<>(result, pageable, recordsFromDb.getTotalElements());
     }
 

src/main/java/com/ainigma100/departmentapi/specification/DepartmentSpecification.java

@@ -0,0 +1,51 @@
+package com.ainigma100.departmentapi.specification;
+
+import com.ainigma100.departmentapi.dto.DepartmentSearchCriteriaDTO;
+import com.ainigma100.departmentapi.entity.Department;
+import jakarta.persistence.criteria.*;
+import org.springframework.data.jpa.domain.Specification;
+import org.springframework.util.StringUtils;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Build a Specification<Department> from DepartmentSearchCriteriaDTO.
+ * - departmentCode: prefix match (case-insensitive)
+ * - departmentName: contains match (case-insensitive)
+ * - departmentDescription: contains match (case-insensitive)
+ *
+ * Extend this class if you want more operators (equals, ranges, enums, etc).
+ */
+public final class DepartmentSpecification {
+
+    private DepartmentSpecification() {}
+
+    public static Specification<Department> fromCriteria(DepartmentSearchCriteriaDTO criteria) {
+        return (Root<Department> root, CriteriaQuery<?> query, CriteriaBuilder cb) -> {
+            List<Predicate> predicates = new ArrayList<>();
+
+            if (criteria == null) {
+                return cb.conjunction();
+            }
+
+            // departmentCode: prefix match (deptCode starts with value), case-insensitive
+            if (StringUtils.hasText(criteria.getDepartmentCode())) {
+                predicates.add(cb.like(cb.lower(root.get("departmentCode")), criteria.getDepartmentCode().toLowerCase() + "%"));
+            }
+
+            // departmentName: contains, case-insensitive
+            if (StringUtils.hasText(criteria.getDepartmentName())) {
+                predicates.add(cb.like(cb.lower(root.get("departmentName")), "%" + criteria.getDepartmentName().toLowerCase() + "%"));
+            }
+
+            // departmentDescription: contains, case-insensitive
+            if (StringUtils.hasText(criteria.getDepartmentDescription())) {
+                predicates.add(cb.like(cb.lower(root.get("departmentDescription")), "%" + criteria.getDepartmentDescription().toLowerCase() + "%"));
+            }
+
+            // Combine predicates (AND)
+            return predicates.isEmpty() ? cb.conjunction() : cb.and(predicates.toArray(new Predicate[0]));
+        };
+    }
+}